android简易的本地音乐播放器

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

private MediaPlayer mediaPlayer=new MediaPlayer();
EditText editText;
String a="";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button start=(Button)findViewById(R.id.start);
Button stop=(Button)findViewById(R.id.stop);
Button pause=(Button)findViewById(R.id.pause);
Button select=(Button)findViewById(R.id.select);
editText=(EditText)findViewById(R.id.edit);
start.setOnClickListener(this);
stop.setOnClickListener(this);
pause.setOnClickListener(this);
select.setOnClickListener(this);
if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)!= PackageManager.PERMISSION_GRANTED){
ActivityCompat.requestPermissions(MainActivity.this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
}

}

private void sing(){
a= editText.getText().toString();       //获取输入内容
Toast.makeText(this,a,Toast.LENGTH_SHORT).show();
initMediaPlayer();
}
private void initMediaPlayer(){
try {
File file=new File(Environment.getExternalStorageDirectory(),"kgmusic/download/"+a+".mp3");   //手机根目录下的文件
mediaPlayer.setDataSource(file.getPath());
mediaPlayer.prepare();
}catch (Exception e){
e.printStackTrace();
}
}

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
switch (requestCode){
case 1:
if (grantResults.length>0&&grantResults[0]==PackageManager.PERMISSION_GRANTED){

}
else {
Toast.makeText(this,"you denied the permission",Toast.LENGTH_SHORT).show();
finish();
}
break;
default:
break;
}

}

public void onClick(View v){
switch (v.getId()){
case R.id.start:
if(!mediaPlayer.isPlaying()){
mediaPlayer.start();
}
break;
case R.id.stop:
if (mediaPlayer.isPlaying()){
mediaPlayer.reset();
initMediaPlayer();
}
break;
case R.id.pause:
if (mediaPlayer.isPlaying()){
mediaPlayer.pause();
}
break;
case R.id.select:
sing();
break;
default:
break;
}
}
protected void onDestroy(){
super.onDestroy();
if (mediaPlayer!=null){
mediaPlayer.stop();
mediaPlayer.release();
}
}
}